Commercial aircraft manufacturers are continuously trying to reduce the amount of noise that aircrafts produce for a multitude of reasons. Major contributors include shockcell noise, buzzsaw noise, boundary layer noise, and other flow-induced noise such as that caused by airflow over the pilot windshield, cavities (e.g., wheel wells), or due to seal issues on doors, wing to body joints, or flap seals. Extended periods of exposure to aircraft noise is a recognized form of air pollution, causing health concerns to humans and animals in areas around airports. In addition, noise is a concern for passengers and flight crews, which experience long-term exposure to in-flight noise. There are even regulations that limit the effective perceived noise level (EPNL) that an aircraft can emit.
Microphones are essential tools used by aeroacousticians to locate, understand and mitigate the impact of noise sources on aircrafts. Such microphones, especially those used for in-flight measurements, can be subject to extreme conditions including high pressures, large changes in temperature, and moisture. Dynamic pressure arrays require small sensing elements, high bandwidth, and close spacing in order to adequately resolve the time and length scales of interest in flow, while aeroacoustic phased arrays require large channel counts to be effective. In terms of performance, these sensors must be able to sense large sound pressure levels without distorting, possess a moderate noise floor, and the sensitivity must be known precisely within a set bandwidth.
Due to the demanding conditions in which aircraft microphones must perform, and their high performance requirements, their costs can be high and the associated costs can hinder the ability to obtain needed measurements. Even with their high cost, commercial sensors are still often constrained by the quality and type of measurements they can obtain. In designing a sensor, additional factors that need to be taken into account include the size of the sensor, the sensor package, and external power and signal conditioning requirements.